1. Field of the Invention
The present invention relates to an oxide superconducting material for use in various superconductivity application apparatus and superconducting devices.
2. Description of the Prior Art
Up to the present, metal or alloy superconducting materials, intermetallic compound superconducting materials, etc. have already been put into practical use as superconducting materials. The superconducting materials are used for production of coils for superconducting magnets, electronics devices such as a Josephson device, etc. and are expected to realize applications particularly to a Superconducting Quantum Interference Device (=SQUID) and a precision measurement technique, utilizing the merits of high sensitivity, high precision and low noise properties of a Josephson junction, and also to an electronic computer, taking advantage of high speed responsibility and low electric power consumption properties of the Josephson junction.
It is desired that a superconductivity transition temperature Tc of a superconducting material is as high as possible. Since an oxide superconductor of La--Ba--Cu--O system having a Tc around 30 K. was found, there are successively found oxide superconductors of Ba--Y--Cu--O system having a Tc around 90 K., Bi--Sr--Ca--Cu--O system having a Tc around 110 K., Tl--Ba--Ca--Cu--O system having a Tc around 120 K., etc. These findings of the materials having Tc far exceeding a liquid nitrogen temperature are further enhancing expectations for use as practical materials.
For applying a superconducting material to an electronics device, it is preferred that the maximum temperature in the entire process for production is as low as possible. It is also important that the critical current density Jc is as large as possible, from the viewpoint of wiring materials. In a Tl--Ba--Ca--Cu system superconductor having not lower than 100 K. superconductivity transition temperature, it is necessary to carry out firing at a temperature of 890.degree.-910.degree. C. for obtaining a higher Jc. Any firing at a lower temperature does not complete sintering and so causes a lower Jc.